In the prior art, copolyesters of various diols with mixtures of terephthalic acid and isophthalic acid are well-known as shown in U.S. Pat. No. 2,965,613. If the isophthalic acid in the terephthalate copolyesters is replaced with tertiary butyl isophthalic acid, many unexpected advantages are gained such as: reduced tendency to crystallize, improved solubility in solvents, higher glass transition temperatures, and higher melt viscosities.
Incorporation of t-butyl isophthalic acid in the copolyesters in the place of isophthalic acid provides high glass transition temperatures. Such resins are particularly useful in applications in which it may be desirable to sterilize plastic articles made of the resins.
The incorporation of even relatively small amounts of t-butyl isophthalic acid (1 to 7 percent) provides copolyesters which have a greatly reduced tendency to crystallize. These resins are useful in molding applications. Copolyesters containing moderate amounts of t-butyl isophthalic acid are considerably more soluble than their isophthalic acid analogs. Such resins may be useful in solution coatings, solution adhesives and in melt adhesives.
In addition to new copolyester resins, the invention relates to products made of the resins, such as melt adhesives, hot melt adhesives, solutions, coatings, molded products, films and fibers.